Rayed Keyhole Limpet
Fissurella nimbosa (Linnaeus, 1758)
The Rayed Keyhole Limpet (there is no official vernacular name- suggested by Harry Lee) was unknown as a live species in North America until two shell were found in 2017 in Hobe Sound. I've found three versions on S. Hutchinson Island beaches. Below are two shells-- the shell on the right has been damaged.